The present invention relates generally to electric vehicles, and more particularly, to improved control methods that control a high efficiency distributed staged power system used in electric and hybrid electric vehicles.
The assignee of the present invention designs and develops electric vehicles and power systems for use therein. Prior art related to power systems for electric vehicles include single-module-level designs and power modules interconnected for current sharing and reliability. There are a variety of documents, including patents and articles, that describe single, high-efficiency DC-to-DC converters. Other documents discuss the interconnecting the power modules to achieve current sharing and reliability.
Prior art distributed power systems typically utilize either a single bulk power supply or multiple parallel power modules configured in a current share mode. However, power electronics are now being incorporated in to electric and hybrid electric vehicles that require very high efficiency power conversion in order to maintain an acceptable driving range. The requirement is even more severe in a hybrid electric vehicle, where the auxiliary load is quite large due to the increased numbers of fans and pumps compared with an electric vehicle.
Prior art power systems have low efficiency when load demand drops. This is true for either the single, large, bulk power supply or with multiple-parallel power modules, configured in a current share mode. In the multiple-parallel power module system, with all modules equally sharing the load current, each module provides only a small fraction of its overall load capability most of the time. The well-known efficiency versus load characteristics of switching power supplies indicates that operation at light load results in inefficient operation.
The present control methods have been developed to control a high efficiency distributed staged power system which is disclosed in U.S. patent application, Ser. No. 09/345,278, filed Jun. 30, 1999, entitled "High Efficiency, Distributed Staged Power System Architecture for Electric Vehicle Accessories Power", and which is assigned to the assignee of the present invention. For reference purposes, the contents of this patent application are incorporated herein in its entirety.
It would therefore be desirable to have improved control methods that may be used to control a high efficiency distributed staged power system.